Laser Pyrolysis

Since the pioneering work of Cannon and co-workers on the continuous production of nanometric powders by laser-induced processes, different powders suchas Si, SiC, Si3N4 and a Si/C/N composite have been prepared under a variety of conditions with sizes ranging from 5 to 20 nm. The method involves heating a flowing mixture of gases with a continuous wave carbon dioxide laser, which initiates and sustains a chemical reaction. Above a certain pressure and laser power, a critical concentration of nuclei is reached in the reaction zone, which leads to homogeneous nucleation of particles that are further transported to a filter by an inert gas. Three characteristics of this method must be emphasized: (a) the small particle size, (b) the narrow particle size distribution, and (c) the nearly absence of aggregation.